The present invention relates to a method for casting objects, and more particularly, a method for casting railroad wheels using an improved hub core assembly.
The preferred method for manufacturing cast steel railroad wheels is a bottom pressure casting foundry operation wherein molten steel under pressure is forced upwardly into a machined graphite mold. The mold is thereby filled with molten steel from the bottom upwardly. This bottom pressure casting operation eliminates many of the concerns associated with traditional top pouring of molten steel into molds in foundry operations such as splashing and insufficient filling.
In the bottom pressure casting of railroad wheels, the top half or cope of the mold is usually a graphite block wherein the top portion or front face of the object beign cast is machined. The bottom half or drag of the mold is also usually a graphite block wherein the bottom portion or rear face of the object being cast is machined. A radially central opening is present in the cope section of the mold, and a complimentary radially central opening is present in the drag of the mold. When the cope section and drag section are combined to form a complete mold, such complete mold is positioned at a pouring station wherein molten steel is forced upwardly into the cavity in the mold to form the railroad wheel. As set forth in detail in U.S. Pat. No. 5,919,392, a ladle of molten steel is placed within a holding tank, and the tank is covered in a manner to seal the ladle in the holding tank. A pouring tube extends downwardly into the molten steel in the ladle and also extends upwardly to the top of the structure at the pouring station. Such pouring tube is typically comprised of a ceramic material as it must withstand the temperatures of the molten steel.
A stopper pipe is positioned in the central opening in the cope and drag sections of each graphite mold. Such stopper pipe includes a metal, usually steel, pipe section and an end stopper head, which is usually comprised of a refractory material such as a resin set sand. Upon the pressurization of the holding tank, the molten steel is forced upwardly through the pouring tube and into the mold cavity to form the railroad wheel. A plurality of risers are usually provided in the cope section of the mold such that additional molten metal can be held as necessary to downwardly fill into the mold during cooling and solidification of the railroad wheel just after pouring. Upon filling of the mold cavity and risers, the pressure is decreased to stop the metal pouring while simultaneously the stopper pipe is extended downwardly to have the end stopper head engage and seal the opening at the bottom of the mold cavity in the drag section. The graphite mold is then moved from the pouring station allowing sufficient time for the steel to solidify before the cope and drag sections are separated.
It is understood that a separate stopper pipe is required for each graphite mold, since the molten metal of the object being cast, usually a railroad wheel, comes in contact with the metal section of the stopper pipe, thereby engaging and melting it. This area of the object being cast, typically a railroad wheel, is subsequently removed to form the hub section of the railroad wheel.
It is desirable to eliminate the use of a separate stopper pipe for each object being cast in the graphite mold.